Mr Trump also mercilessly taunted and mocked Mr Carson on the campaign trail, particularly over Mr Carson's claim that he once tried to stab a fellow student but that the boy's belt buckle prevented the knife from breaking the skin.

But Mr Trump later sided with Mr Carson over a dispute in Iowa, when Senator Ted Cruz's campaign wrongly told voters that Mr Carson had dropped out of the race before the state's February 1 caucuses.

Mr Carson said he believed the billionaire real estate mogul will be able to put aside his caustic, controversial rhetoric that has become a hallmark of his public appearances.

"There are two Donald Trumps. There's the Donald Trump that you see on television and who gets out in front of big audiences, and there's the Donald Trump behind the scenes," Mr Carson told Fox.

"They're not the same person. One's very much an entertainer, and one is actually a thinking individual."